In the field of hybrid drive systems, it is generally known for the motor vehicle to be driven purely electrically by means of the electric machine or driven exclusively by means of the internal combustion engine. It is also known, upon start-up of the motor vehicle, that is to say in the event of a key-initiated start, for the internal combustion engine to be started by means of the electric machine and for the motor vehicle to be driven by means of the internal combustion engine, or, upon start-up of the motor vehicle, for only the electric machine to be used to drive the motor vehicle and, if appropriate, for the internal combustion engine to be started during travel by being drag-started by means of the electric machine.
A disadvantage of the internal combustion engine being started by drag-starting during travel is that, during said process, the traction battery of the motor vehicle is subject to intense load and under certain conditions the traction battery can sustain permanent damage. Furthermore, the internal combustion engine is generally subject to higher wear when started by drag-starting by means of the electric machine than when started by cranking by means of the electric machine, such that under certain conditions, such a start by drag-starting should be avoided.
DE 10 2012 000 036 A1 discloses a method for the start-up of an internal combustion engine of a hybrid drive, in which method a torque for the start-up of the internal combustion engine is set as a function of a temperature of the internal combustion engine. A disadvantage here is that consideration is not given to all influential variables and start-up variations that have a significant influence on wear of the internal combustion engine.
DE 102 46 978 A1 discloses a method for the starting of a drive unit of a motor vehicle, in which method different modes for the starting of the internal combustion engine are set as a function of a temperature of the internal combustion engine. A disadvantage here is that consideration is not given to the wear in the event of drag-starting by means of the electric motor.